          (add-standing-charge-if-selected operation tariff))))
 
 (defmethod apply-tariff :simple [tariff measurements operation]
-  (let [{:keys [cost_per_kwh]} tariff
+  (let [{:keys [cost_per_kWh]} tariff
         total-consumption (reduce + (map :value (filter #(number? (:value %)) (measurements/parse-measurements measurements))))]
     (->> total-consumption
-         (* cost_per_kwh)
+         (* cost_per_kWh)
          (add-standing-charge-if-selected operation tariff))))
 
 (defmethod apply-tariff :none [_ _ _]

    off          (* off-peak-cost off)))

(defmethod apply-tariff :on-off-peak [tariff measurements operation]
  (let [{:keys [cost_per_kwh off_peak_periods
                cost_per_on_peak_kwh cost_per_off_peak_kwh]} tariff]
    (->> measurements
         measurements/parse-measurements

  (fn [tariff _ _]
    (condp #(%1 %2) tariff
      :off_peak_periods :on-off-peak
      :cost_per_kWh     :simple
      :none)))

(defn day->on-off-periods
